diff --git a/lib/AmsDecoder/include/crc.h b/lib/AmsDecoder/include/crc.h
index 2a29070a..4a2c84d1 100644
--- a/lib/AmsDecoder/include/crc.h
+++ b/lib/AmsDecoder/include/crc.h
@@ -12,6 +12,6 @@
 
 uint16_t crc16(const uint8_t* p, int len);
 uint16_t crc16_x25(const uint8_t* p, int len);
-uint16_t crc16_ccit(const uint8_t* p, int len);
+uint16_t crc16_1021(const uint8_t* p, int len);
 
 #endif
diff --git a/lib/AmsDecoder/src/crc.cpp b/lib/AmsDecoder/src/crc.cpp
index 2626cf32..52825c1e 100644
--- a/lib/AmsDecoder/src/crc.cpp
+++ b/lib/AmsDecoder/src/crc.cpp
@@ -34,20 +34,23 @@ uint16_t crc16 (const uint8_t *p, int len) {
     return crc;
 }
 
-uint16_t crc16_ccit(const uint8_t *p, int len)
+uint16_t crc16_1021(const uint8_t *p, int len)
 {
-    int  crc;
-    char i;
-    crc = 0;
-    while (len--) {
-        uint8_t i;
-      	crc = crc ^ (uint8_t) *p++ << 8;
-		for (i = 0 ; i < 8 ; ++i) {
-			if (crc & 0x8000)
-				crc = crc << 1 ^ 0x1021;
-			else
-				crc = crc << 1;
+	uint16_t crc = 0x0000;
+	for(uint16_t i = 0; i < len; i++) {
+		uint16_t mask = 0x80;
+		while(mask > 0) {
+			crc <<= 1;
+			if (p[i] & mask) {
+				crc |= 1;
+			}
+			mask>>=1;
+			if (crc & 0x10000) {
+				crc &= 0xffff;
+				crc ^= 0x1021;
+			}
 		}
-   }
-   return (crc);
+	}
+	return crc;
+
 }